1. Field of the Invention
The present invention relates to 1,3,4 -trisubstituted-5-oxo-2-pyrazoline salts in which the 4-position is substituted with a pyridine ring with the bonding being to the nitrogen atom of the pyridine ring and processes for producing the salts.
2. Description of the Prior Art
It is well-known that 1,3-disubstituted-5-oxo-2-pyrazolines are important compounds as magenta color-forming couplers for color photographic light-sensitive materials based on the subtractive process for color formation, and that these compounds are also useful as intermediates in preparing various medicines and dyes. For example, when a conventional color photographic silvr halide light-sensitive material containing a 1,3-disubstituted-5-oxo-2-pyrazoline is color developed, after exposure, the coupler couples with an oxidized para-phenylenediamine-type color developing agent to form a corresponding azomethine dye. It is well-known that such a 1,3-disubstituted-5-oxo-2-pyrazoline coupler theoretically requires for moles of silver halide as the oxidizing agent to form one mole of an azomethine dye in the color-forming coupling reaction. On the contrary, a 1,3,4-trisubstituted-5-oxo-2-pyrazoline having in the 4-position a substituent which is easily releasable on coupling with an oxidized color-developing agent can theoretically form one mole of dye using only two moles of silver halide.
For this reason, 5-oxo-2-pyrazolines having in the 4-position a releasable substituent or a precursor group which can provide a releasable substituent are particularly important compounds in the production of color photographic light-sensitive materials.